1. Field of the Invention
The present invention relates generally to a hydraulic cylinder controlling apparatus, and more particularly to an apparatus for controlling a hydraulic single acting cylinder having a piston subjected to a continual unidirectional external force. The controlling apparatus is used for the control of automobile clutches, for example.
2. Description of the Related Art
There have recently been proposed various apparatuses for effecting an automatic gear shaft in a conventional automobile power transmission of the type having a clutch and a transmission gear unit so as to reduce loads on a driver as well as to provide improved mileage. In this instance, it is necessary to automatically control the clutch operations when the clutch is in a partly engaged or half-clutched condition. Japanese Patent Laid-open Publication No. 58-146722 discloses an apparatus for controlling a hydraulic single acting cylinder connected with the clutch for actuating the latter. The disclosed apparatus includes three solenoid operated directional control valves disposed in a hydraulic supply line or passage and a hydraulic return line or passage and controlled in response to the output from a control unit.
Since these solenoid operated valves comprise directional control valves having two ports and two distinct positions of the conventional type and having no means for controlling the hydraulic pressure, the cylinder piston reciprocates at a fixed speed. As a result, a great shock is generated when stopping the piston at a desired position and sometimes it becomes difficult to stop the cylinder accurately at the desired position due to overshooting caused by delayed response of the solenoid operated valves.